In these times of heightened security, there are many instances when particular geographic areas may need to be placed under surveillance to protect potential targets from terrorist attacks or as an adjunct to military operations.
When an object is imbedded in a medium such as rain or fog, the presence of scatterers in the medium causes the image of the object to appear indistinct or blurred, making object detection difficult. One aspect of man-made objects that may assist in their detection, however, is that they emit and reflect near-infrared radiation that is more highly polarized than does natural background that may include trees, brush grass or terrain.
There are two broad categories of infrared systems designed for military use; namely, scanning system and staring system. However, infrared sensors for extant missile seekers and forward-looking infrared (FLIR) sensors lack the capability for detecting the polarization orientation of the incident radiation, i.e. they respond to any polarization orientation vector of the incident radiation. Studies have shown that the capability to detect and analyze the polarization orientation of near-infrared radiation emanating or reflecting from targets and background scenery can provide a potential means for improving the detection and discrimination of the targets in military systems. Infrared instrumentation having this feature would also have potential commercial applications in areas such as pattern recognition, materials characterization and analysis.
Thus, one way to improve the performance of target detection system is to utilize polarized infrared signatures of a given scenery. What renders this possible is that polarization properties are independent of target-background contrast (i.e. polarization properties are distinct even when there is no temperature difference between the target and the background) and of normal infrared target and clutter temperature fluctuations (i.e. standard deviation of temperature). As is well-known, the formal characterization of an electromagnetic wave that may be linear, elliptical or circular is accomplished with the derivation of the four Stokes parameters.